1. Field of the Invention
The present invention relates to a communication control device and a communication control method, and more specifically, to a communication mode switching in a communication via a public line between computers each handling facsimile data for a facsimile communication and other data for a data communication.
2. Description of the Prior Art
There have been available a voice communication, a facsimile communication and a data communication as communications using the public line, such as, the telephone line. Recently, data communication modems capable of handling facsimile data as well have been rapidly developed and commercially available. However, in the conventional communication control devices incorporating those data communication modems, once a facsimile communication mode is set, a data communication mode can not be effected until the line is once opened and another call is made. Specifically, once the facsimile communication mode is set, a communication procedure pursuant to CCITT (International Telegraph and Telephone Consultative Committee) Recommendation T. 30 is performed between transmitter-side and receiver-side communication control devices or terminals.
The conventional facsimile communication procedure will be explained hereinbelow with reference to a flowchart shown in FIG. 5.
Step S1 executes a phase A, wherein a call is made and a line is connected or established between the transmitter-side and receiver-side terminals. Specifically, a caller switches a communication mode from a data communication mode to a facsimile communication mode and then dials a number for connection to the receiver-side terminal. In response to this, the receiver-side terminal automatically closes the direct current loop to establish the line for the facsimile communication. The procedure then advances to a phase B. As appreciated, in case of the manual calling/receiving operation, a caller offhooks a handset and dials the number for connection to the receiver-side terminal, and then performs a voice communication with a receiver upon offhook of a handset by the receiver. Thereafter, the facsimile communication mode is established between the transmitter-side and receiver-side terminals through the given manual operation. The procedure then advances to the phase B.
Step S2 executes the phase B, wherein transmission of facsimile or image data is set ready. Specifically, the transmitter-side and receiver-side terminals perform preparation of transmission and reception, display and determination of terminal constants, confirmation of a synchronous condition, and the like. The procedure then advances to a phase C.
Step S3 executes the phase C, wherein transmission of the image data, confirmation thereof, holding of the synchronous condition, and the like are performed. Upon completion of transmission of one-page image data, the procedure advances to a phase D.
Step S4 executes the phase D, wherein message transmission, confirmation thereof, and the like are performed. If image data transmission is continued (step S4-1), the procedure returns to step S2 (phase B) or step S3 (phase C) depending on an image attribute of one-page image data to be transmitted next (step S4-2), so as to repeat image data transmission. On the other hand, after transmission of image data of the final page, the procedure advances to step S5. Step S5 executes a phase E, wherein the line is opened or disconnected.
Hereinbelow, the phase D will be explained in further detail with reference to FIGS. 6-8.
FIG. 6 is a diagram showing a communication sequence between the transmitter-side and receiver-side terminals, wherein an image attribute of one-page image data to be transmitted next (hereinafter referred to as "next one-page image data") and that of one-page image data transmitted immediately before (hereinafter referred to as "last one-page image data") are the same with each other. As shown in FIG. 6, the transmitter-side terminal transmits a multi-page signal (MPS) 52 after completion of transmitting one-page image data 51. Upon detection of MPS 52, the receiver-side terminal sends back a message confirmation signal (MCF) 53. This causes both the transmitter-side and receiver-side terminals to be set for the phase C, that is, for transmission of the next one-page image data.
FIG. 7 is a diagram showing a communication sequence between the transmitter-side and receiver-side terminals, wherein an image attribute of the next one-page image data and that of the last one-page image data differ from each other. As shown in FIG. 7, the transmitter-side terminal transmits an end-of-message signal (EOM) 62 after completion of transmitting one-page image data 61. Upon detection of EOM 62, the receiver-side terminal sends back a message confirmation signal (MCF) 63. This causes both the transmitter-side and receiver-side terminals to be set for the phase B, that is, for preparation of transmission of the next one-page image data.
FIG. 8 is a diagram showing a communication sequence between the transmitter-side and receiver-side terminals, wherein image data of the final page are transmitted. As shown in FIG. 8, the transmitter-side terminal transmits an end-of-procedure signal (EOP) 72 after completion of transmitting one-page image data 71. Upon detection of EOP 72, the receiver-side terminal sends back a message confirmation signal (MCF) 73. This causes both the transmitter-side and receiver-side terminals to be set for the phase E so that the line is opened.
As appreciated from the foregoing explanation, in the conventional communication system, although the image data of a plurality of pages can be transmitted without disconnecting the line, once the communication mode is switched to the facsimile communication mode, the line is unconditionally disconnected when transmission of the image data of all the pages has been finished. Accordingly, even when the data communication is desired after the facsimile communication, it is impossible to perform the data communication until a call is again made to establish the line for the data communication. In other words, the manual operation is always necessary for performing the data communication after the facsimile communication.